Abbreviations used herein:                CBR Constant Bit Rate        VBR Variable Bit Rate        TDM Time Division Multiplex        LLC loss-less compression codec        VBR variable bit rate        RT Real Time        CAC Call Admission Control        BS Base Station        BTS Base Transceiver Station        BSC Base Station Controller        GSM Global System for Mobile communications        VAS Voice Activity Status        
Traditional telephone networks transmit multiple telephone calls over a single channel using time division multiplex (TDM) technology. When TDM is used to transmit telephone calls, the communication channels transmits the data at a constant bit rate (CBR).
Telephone calls can also be transmitted over packet networks. Loss-less compression codecs (LLC) can be used to packetize telephone calls for transmission over a packet network While traditional TDM transmits data at a CBR, LLCs produce a variable bit rate (VBR) data stream.
Typically when multiple streams of VBR traffic are transmitted over a particular link, the amount of bandwidth allocated for each channel is based on the expected average bit rate of the various channels. In many situations the bit rate of the VBR sources are not correlated and hence averages and expectations are a reasonable approach to allocating bandwidth for such links. In many situations, the bandwidth allocated to a VBR connection is established at call set up time. The bandwidth allocation remains constant for all VBR calls which have the same characteristics.
The VBR data streams produced by LLCs operating on voice calls have some special characteristics. Such channels in effect emulate Constant Bit Rate (CBR) channels. Furthermore, they must have a very low error bit rate since they are a replacement for TDM links which have a very low bit error rate. In a typical VBR link, if bandwidth usage exceeds that which can be accommodated over a particular link, a policing mechanism kicks in, and in general this causes higher error rates. The VBR data streams produced by LLCs operating on voice calls generally can not tolerate high error rates.
The present invention also addresses the problem that occurs when a VBR communication link is oversubscribed. That is, the present invention addresses the problem that occurs when there is not enough bandwidth to handle all of the calls destined for a particular link.
In many communication links, a Call Admission Control (CAC) system is used to allocate calls to various links. Typically CAC systems allocate bandwidth for each call when the call is set up. Bandwidth is allocated based on a formula that takes into account the nature of the call in a conventional system, the bandwidth allocation formula does not take into account the amount of bandwidth actually being used by other calls that are being handled by the system at that particular time.